Maerl beds are free-living, non-geniculate coralline algae habitats which form biogenic reefs with high micro-scale complexity supporting a diversity and abundance of rare epifauna and epiflora. These habitats are highly mobile in shallow marine environments where substantial maerl beds co-exist with siliciclastic sediment, exemplified by our study site of Galway Bay. Coupled hydrodynamic-wave-sediment transport models have been used to explore the transport patterns of maerl-siliciclastic sediment during calm summer conditions and severe winter storms. The sediment distribution is strongly influenced by storm waves even in water depths greater than 100 m. Maerl is present at the periphery of wave-induced residual current gyres during storm conditions. A combined wave-current Sediment Mobility Index during storm conditions shows correlation with multibeam backscatter and surficial sediment distribution. A combined wave-current Mobilization Frequency Index during storm conditions acts as a physical surrogate for the presence of maerl-siliciclastic mixtures in Galway Bay. Both indices can provide useful integrated oceanographic and sediment information to complement coupled numerical hydrodynamic, sediment transport and erosion-deposition models.
Sea-level Rise, Coastal Flooding, and Storm Events
This paper aims to inform forward-planning policies in the face of sea-level rise due to climate change, focusing on the choice of reducing the vulnerability of property at risk through managed retreat or protection behind seawalls. This adaptation is important not only to reduce the cost of future damage but also to maintain the beaches which are an attractive feature for tourism, of vital importance for coastal areas. Some 421 residents with main and secondary homes were surveyed in Hyères-les-palmiers in the Var department (Southeast France). The survey sought to compare the willingness of residents to contribute financially to building a seawall or to relocating sea-front property. Preferences depend both on common variables and variables specific to the proposed arrangement. They reveal common concerns focused on effectiveness and the determining factor of property ownership. The results also show some awareness of the long-term advantages of managed retreat, despite some opposition from older people, who are also more skeptical about the reality of the risk incurred.
Many of the world's largest cities face risk of sea-level rise (SLR) induced flooding owing to their limited elevations and proximities to the coastline. Within this century, global mean sea level is expected to reach magnitudes that will exceed the ground elevation of some built infrastructure. The concurrent rise of coastal groundwater will produce additional sources of inundation resulting from narrowing and loss of the vertical unsaturated subsurface space. This has implications for the dense network of buried and low-lying infrastructure that exists across urban coastal zones.
Here, we describe a modeling approach that simulates narrowing of the unsaturated space and groundwater inundation (GWI) generated by SLR-induced lifting of coastal groundwater. The methodology combines terrain modeling, groundwater monitoring, estimation of tidal influence, and numerical groundwater-flow modeling to simulate future flood scenarios considering user-specified tide stages and magnitudes of SLR.
We illustrate the value of the methodology by applying it to the heavily urbanized and low-lying Waikiki area of Honolulu, Hawaii. Results indicate that SLR of nearly 1 m generates GWI across 23% of the 13 km2 study area, threatening $5 billion of taxable real estate and 48 km of roadway. Analysis of current conditions reveals that 86% of 259 active cesspool sites in the study area are likely inundated. This suggests that cesspool effluent is currently entering coastal groundwater, which not only leads to degradation of coastal environments, but also presents a future threat to public health as GWI would introduce effluent at the ground surface.
The El Niño-Southern Oscillation is the dominant mode of interannual climate variability across the Pacific Ocean basin, with influence on the global climate. The two end members of the cycle, El Niño and La Niña, force anomalous oceanographic conditions and coastal response along the Pacific margin, exposing many heavily populated regions to increased coastal flooding and erosion hazards. However, a quantitative record of coastal impacts is spatially limited and temporally restricted to only the most recent events. Here we report on the oceanographic forcing and coastal response of the 2015–2016 El Niño, one of the strongest of the last 145 years. We show that winter wave energy equalled or exceeded measured historical maxima across the US West Coast, corresponding to anomalously large beach erosion across the region. Shorelines in many areas retreated beyond previously measured landward extremes, particularly along the sediment-starved California coast.
Sea level rise will have significant impacts on many coastal resources. Waves are an important resource in California, where they support the recreation of 1.1 million surfers who inject millions of dollars into local economies. The impacts of sea level rise on wave resource quality, however, are unknown. By examining the local knowledge of more than one thousand California surfers collected through an online survey, this study extrapolates their evaluations to estimate the susceptibility of California surf-spots to sea level rise based on the principle of tidal extrapolation. Vulnerability classifications are derived from the relationship between wave quality, tide effects, and sea floor conditions. Applying these classifications to 105 surf-spots in California evaluated by multiple respondents, we project that as a result of sea level rise by 2100: 16% of surf-spots are Endangered due to drowning; 18% are Threatened, but could adapt if natural shoreline processes are not impeded; and 5% might improve as rising sea levels increase the likelihood they will experience optimal conditions. These projections are significant not only for the many surfers who depend on surf-spots, but also for the coastal communities who rely on the availability of high quality wave resources. Results from this study also have important implications for when and how managers might take surf-spot quality and vulnerability into consideration through coastal adaptation. Lastly, this study establishes a baseline of wave resource quality in California and suggests that this baseline will shift as wave quality changes over the coming century.
We depict the relative sea-level rise scenarios for the year 2100 from four areas of the Italian peninsula. Our estimates are based on the Rahmstorf (2007) and IPCC-AR5 reports 2013 for the RCP-8.5 scenarios (www.ipcc.ch) of climate change, adjusted for the rates of vertical land movements (isostasy and tectonics). These latter are inferred from the elevation of MIS 5.5 deposits and from late Holocene sea-level indicators, matched against sea-level predictions for the same periods using the glacio-hydro-isostatic model of Lambeck et al. (2011). We focus on a variety of tectonic settings: the subsiding North Adriatic coast (including the Venice lagoon), two tectonically stable Sardinia coastal plains (Oristano and Cagliari), and the slightly uplifting Taranto coastal plain, in Apulia. Maps of flooding scenarios are shown on high-resolution Digital Terrain Models mostly based on Lidar data. The expected relative sea-level rise by 2100 will change dramatically the present-day morphology, potentially flooding up to about 5500 km2 of coastal plains at elevations close to present-day sea level.
The subsequent loss of land will impact the environment and local infrastructures, suggesting land planners and decision makers to take into account these scenarios for a cognizant coastal management. Our method developed for the Italian coast can be applied worldwide in other coastal areas expected to be affected by marine ingression due to global climate change.
Mitigation of anthropogenic greenhouse gases with short lifetimes (order of a year to decades) can contribute to limiting warming, but less attention has been paid to their impacts on longer-term sea-level rise. We show that short-lived greenhouse gases contribute to sea-level rise through thermal expansion (TSLR) over much longer time scales than their atmospheric lifetimes. For example, at least half of the TSLR due to increases in methane is expected to remain present for more than 200 y, even if anthropogenic emissions cease altogether, despite the 10-y atmospheric lifetime of this gas. Chlorofluorocarbons and hydrochlorofluorocarbons have already been phased out under the Montreal Protocol due to concerns about ozone depletion and provide an illustration of how emission reductions avoid multiple centuries of future TSLR. We examine the “world avoided” by the Montreal Protocol by showing that if these gases had instead been eliminated in 2050, additional TSLR of up to about 14 cm would be expected in the 21st century, with continuing contributions lasting more than 500 y. Emissions of the hydrofluorocarbon substitutes in the next half-century would also contribute to centuries of future TSLR. Consideration of the time scales of reversibility of TSLR due to short-lived substances provides insights into physical processes: sea-level rise is often assumed to follow air temperature, but this assumption holds only for TSLR when temperatures are increasing. We present a more complete formulation that is accurate even when atmospheric temperatures are stable or decreasing due to reductions in short-lived gases or net radiative forcing.
Recent eustatic sea level rise (SLR) is one of the most striking manifestations of recent climate change as it directly impacts coastal activities and ecosystems. Although global SLR is well-known, local values differ due to vertical land motion, and changes in atmospheric pressure, ocean currents and temperatures. Although a reliable estimation of local SLR trends is needed to assess coastal zone vulnerabilities and plan adaptation strategies, instrumental records are usually short or sparse, especially in developing countries. Here we show that 210Pb-dated sedimentary records from mangrove saltmarshes can provide useful decadal records of local SLR trends. We quantified sediment accretion rates in sediment cores from remote mangrove saltmarshes of the Yucatan Peninsula. Best SLR records were observed for cores collected near mean sea level (MSL). During most of the XX century the SLR rate ranged from 1-2 mm yr-1, increased to a maximum of 4.5 ± 0.6 mm yr-1 and the acceleration was 0.13 mm yr-2. Assuming either a constant SLR rate or acceleration, by the end of this century MSL level will be 39 cm or 91 cm above the present value. Both coastal infrastructures and ecosystems will be negatively affected by SLR and society will need to adapt relatively fast to the new conditions.
Federal, state, and local governments in the United States, along with land trusts and other nonprofit organizations, have invested significant financial resources in protection of natural lands in coastal areas. As the climate changes, protected lands could provide increased resilience to coastal communities, yet climate change also poses a threat to the continued existence and healthy functioning of these ecosystems. The objectives of this research are to characterize the distribution and types of coastal protected lands in the eastern United States, estimate their exposure to sea level rise, evaluate the potential impact of this exposure on associated ecosystem services, and then discuss appropriate adaptation measures. For this, we construct an inventory of coastal protected lands in shoreline counties of US states along the Atlantic. We summarize their ownership and land cover and evaluate their exposure to a 3-foot (0.91 m) rise in sea level. We find substantial variation in the amount of lands protected in coastal shoreline counties, from a high of 34 percent in Florida to a low of 7 percent in Pennsylvania. Federal ownership is greatest in the South, whereas state ownership dominates in the Mid-Atlantic. Private groups own large shares of protected lands in Maine, New Hampshire, Delaware, and Maryland. Moving south, dominant land covers in protected areas shift from forests to wetlands. We find that one quarter of protected lands in shoreline counties will be affected by 3 feet of sea level rise, with substantial heterogeneity in exposure across states and greater impacts in southern states. Almost 50 percent of federal lands and around 25 percent of state lands will be affected. While substantial proportions of estuarine wetlands and unconsolidated shore (beaches and dunes) are currently protected and provide key coastal ecosystem services, 95 and 91 percent of these protected systems, respectively, will be affected by 3 feet of sea level rise. We discuss the potential consequences and the associated reductions in ecosystem service provisioning from sea level rise in the context of current funding and adaptation planning for conservation. We find that some of the states facing the greatest challenges are those lacking plans and funding. The large heterogeneity in ownership, land covers, and funding across states suggests that adaptation policies for coastal protected lands will need to be tailored to the local context; a one-size-fits-all approach is unlikely to be as effective.
Boston residents are already affected by extreme heat, rain, snow and flooding. These trends will likely continue. The City launched Climate Ready Boston to help Boston plan for the future impacts of climate change.
Climate Ready Boston is an ongoing initiative. We released a comprehensive study report in December 2016 that you can read below. Next, we plan to work with the community and other partners to help advance our vision for a Climate Ready Boston.
Please note: the full report is approximately 120 MB, and includes detailed maps which may increase load-times on mobile devices and older computers. You may download the full-text from the City of Boston's website, shown above.